A three-dimensional effect display, such as an autostereoscopic display, may allow a user to focus on displayed image features in a plane. The same applies to all stereoscopic displays that are based on a substantially planar display surface, whether they employ user-specific viewing devices such as polarizing or time-synchronized eyeglass devices or alternatively, user tracking in the vicinity of the display device. Although the display provides an illusion of three-dimensional content, the user will experience discomfort due to the mismatch of vergence and focus that the stereoscopic planar displays provide.
A three-dimensional display may allow a user to focus on displayed image features that are within a three-dimensional display volume. The image is thus volumetric, and the focus-vergence mismatch is avoided. This situation is beneficial to the user's viewing comfort
Current three-dimensional (volumetric) displays suffer from a number of problems. They are typically either very complex and expensive or only capable of providing very small display volumes. The expense usually is a result from complex mechanical systems employed in providing the image. Another source of excessive cost is the use of e.g. rare-earth ion-doped glass material that is sometimes used in small-scale volumetric display systems.